1. Field of the Invention
This invention relates in general to gate valves, and, more particularly, to a motorized gate valve that can be used as a flush valve in an aircraft waste disposal system, including those systems in which a pressure differential exists between the two sides of the valve.
2. Description of the Related Art
In recent years, efforts have been urdertaken to replace the recirculating waste disposal systems found on vehicles with non-recirculating systems that utilize an on board supply of flushing liquid, usually potable water. For many years, the recirculating waste disposal svstems have been utilized primarily to eliminate the need to carry extra liquid that would be needed for flushing.The recirculating waste disposal system started with a small pre-charge of flushing fluid and utilized any added liquid waste in the flushing process.
As a result of some effort, waste disposal systems have been developed that require only minimal amounts of liquid in the flushing process. These systems permit use of an on-board potable water supply as a source of flushing fluid without imposing severe weight and/or storage penalties. Because the amount and volume of flushing fluid can be small, it is important to have a flush valve that will quickly open and close over a large orifice so that the waste matter will move out of the toilet unit and into the waste line rapidly.
For those waste disposal systems that utilize a pressure differential between the environment of the toilet unit (normally at aircraft cabin pressure) and the exterior of the aircraft in flight, the flush valve must also provide a pressure seal to preserve the pressure differential and to avoid depressurization of the cabin when closed.
Some prior art valves, as in U.S. Pat. No. 4,199,828 to Hellers, have utilized a weighted flapper which opens when the weight of the waste matter and the pressure differential overcome the weight biasing the valve closed.
Other valves have been designed with a diaphragm which occludes a bend in the waste line and acts as a seal, effectively separating the higher pressure toilet unit from the lower pressure waste tank. One such valve is shown in U.S. Pat. No. 4,376,315 to Badger et al.
The diaphragm pinch valve, which is the essence of the Badger et al invention, preferably utilizes a major bend of goose neck shape or trap in the waste discharge line. While in fact diaphragm pinch valves as suggested by Badger et al have been constructed in a straight section of a waste discharge line, such valves are highly susceptible to damage (especially the flexible diaphragm member) from objects impinging on them as waste material is drawn through the valve.
Further, in waste disposal systems utilizing minimal amounts of flushing fluid, the use of a trap would hold waste products in proximity to the toilet unit of the system. In aircraft systems and in vacuum systems generallv, it is preferable to have a direct waste line to the storage tank and it would be advantageous to have a substantially straight, gravity assisted line.
The present invention overcomes the tendencies of these Badger et al type of pinch valves to be damaged by the internal flow of waste materials therethrough by having a relatively short, straight passage directly through the valve with no exposed seals or diaphragms. Accordingly, the passage of objects that would normally damage a Badger et al type of valve would have no effect on a valve made in accordance with the present invention.
In order to provide a waste line that is suitable for low volume flush aircraft systems and one that could easily accommodate a vacuum assisted flushing process, a flush valve is necessary that can maintain a pressure differential when closed and that can quickly open and close a wide aperture so that when the toilet unit of the system is flushed and the waste oroducts and flushing fluid accumulate at the valve, a quickly opened and closed valve can let the pressure differential carry the waste products into the main waste line.
Finally, it should be noted that most prior art valve seals used in gate valves are of the "O" ring or spring loaded type. None of these prior art seals have sufficient comoliance to allow the seal to seal on itself and still not have so much static friction that the sliding gate cannot be withdrawn, without a large driving device from between the seals with the valve in the closed position. Also, currently used prior art seals undergo severe wearing forces and must be reolaced on a regular basis.
The present invention overcomes these noted problems in the prior art seals used in waste system motorized gate valves by disclosing (and claiming) a seal having a design permitting the seal, of rubber-like flexure, to mechanically rotate as the slide gate is moved into the valve closed position, inserted between the seals. As the slide gate is moved to its open position, that is, withdrawn from between the seals, the natural resilience of the elastomer in the seals along with the design of the seals, causes each seal to rotate back mechanically to its original position, each resiliently biased against the other, sealing the passing waste products from entry into the valve housing. This is necessary as the accumulation of waste products in the valve housing is unacceptable from a sanitary standpoint.
Since the seals mechanically rotate in association with the slide gate, the seals experience little to no wearing forces and have a considerably longer life expectancy than prior art seals.